Many expression QTL studies were performed in plants and animals, including humans,[6] non-human primates[7][8] and mice.
[12] The combination of whole-genome genetic association studies and the measurement of global gene expression allows the systematic identification of eQTLs.
The integration of eQTLs with GWAS has led to development of the transcriptome-wide association study (TWAS) methodology.
As is true in all QTL mapping studies, the final steps in defining DNA variants that cause variation in traits are usually difficult and require a second round of experimentation.
This is especially the case for trans eQTLs that do not benefit from the strong prior probability that relevant variants are in the immediate vicinity of the parent gene.
Statistical, graphical, and bioinformatic methods are used to evaluate positional candidate genes and entire systems of interactions.